At least 6,000 people have died since the start of the revolt against Libyan leader Muammar Gaddafi's regime two weeks ago, a spokesman for the Libyan Human Rights League said Wednesday.

"Victims in the whole country were 6,000," Ali Zeidan told reporters in Paris, adding that this included 3,000 in the capital Tripoli, 2,000 in the rebel-held second city Benghazi and 1,000 in other cities.

"This is what people told us, but it can be more," he added.

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Meanwhile, the prosecutor of the International Criminal Court says he is opening a formal investigation into possible crimes against humanity in Libya.

The announcement is an unprecedentedly swift reaction to Gaddafi's violent crackdown on anti-government protests. Prosecutors often take months and sometimes years to decide whether to open an investigation into possible war crimes.

Wednesday's announcement said Prosecutor Luis Moreno-Ocampo has decided to launch the investigation after a "preliminary examination of available information."

The United Nations Security Council on Saturday ordered the court to look into possible crimes in Libya. Moreno-Ocampo only began a preliminary probe Monday.

Elsewhere, a witness says a Libyan warplane struck near the scene of a battle between regime opponents and loyalists of Gaddafi at this eastern oil port.

The warplane from Gaddafi's air force struck a beach near where the two sides were fighting at a university campus in Brega. The witness says the blast raised a plume of sand from a dune but caused no casualties, apparently an attempt to scare off the anti-Gaddafi fighters besieging regime forces in the campus.